We all have times when we do not speak clearly. We may add filler words like "uh" or "you know" to what we say. Or, we may say a sound or word more than once. These are called disfluencies.
People who stutter may have more disfluencies and different types of disfluencies. They may repeat parts of words (repetitions), stretch a sound out for a long time (prolongations), or have a hard time getting a word out (blocks). In short stuttering a failure to articulate or vocalize a sound and thus a word. This often also results in ticks and other odd physical behaviors.
Stuttering is more than just disfluencies. Stuttering also may include anxiety and negative feelings about talking. It may get in the way of how you talk to others and how you present yourself to the rest of the world. You may want to hide your stuttering. So, you may avoid certain words or situations. For example, you may not want to talk on the phone or order food if that makes you stutter more.
Stuttering can change from day to day. You may have times when you are more in control of your speech and times when you stutter more.
Stress or excitement can lead to more stuttering.